Preparation process of glass packaged thermistor

Abstract

The invention discloses a preparation process of a glass packaged thermistor, and relates to the technical field of electronic component manufacturing. Comprising the following steps: S1, chip and lead preparation: providing a semiconductor thermistor chip with an ohmic contact electrode formed on the surface, and providing a pair of metal leads with metal coatings on the surfaces; s2, preparing a glass packaging material; s3, carrying out coating molding and drying; s4, carrying out stepped heat treatment packaging; by optimizing the borosilicate glass component, the thermal expansion coefficient of the borosilicate glass component is between the thermal expansion coefficient of chip ceramic and the thermal expansion coefficient of the metal lead, and by combining with the precisely controlled annealing process, the internal residual stress of the packaging body is greatly reduced, and the anti-cracking performance and the long-term reliability of the product under cold and hot impact are improved.

Description

Technical Field

[0001] This invention relates to the field of electronic component manufacturing technology, specifically to a fabrication process for a glass-encapsulated thermistor. Background Technology

[0002] A thermistor is a semiconductor ceramic element whose resistance changes significantly with temperature. It is widely used in circuits for temperature measurement, compensation, control, and overload protection. To withstand harsh environments such as high temperature, high humidity, and corrosive gases, thermistor chips are often encapsulated for protection.

[0003] Traditional packaging methods mainly include resin packaging, metal casing packaging, and glass packaging. Resin packaging is low in cost, but has poor high-temperature resistance and sealing performance, and is prone to aging and moisture absorption leading to performance drift over long-term use. Metal casing packaging has high reliability, but is bulky, expensive, and has insulation and thermal stress matching issues. Glass packaging, due to its excellent hermeticity, superior insulation properties, good chemical stability, and potential for good thermal expansion coefficient matching with ceramic chips, has become an ideal high-end packaging form.

[0004] However, existing glass encapsulation processes still have some shortcomings: 1) The thermal expansion coefficients between glass powder and the thermistor chip and leads are not well matched, which can easily generate internal stress during high-temperature sealing and subsequent thermal cycling, leading to cracking or performance failure of the package; 2) High temperatures during the encapsulation process can easily cause irreversible deviations in the performance of the thermistor chip (such as B value and resistance value); 3) Improper control of fluidity and wettability during glass sealing can easily lead to defects such as pores and poor wetting, affecting airtightness and mechanical strength.

[0005] Therefore, developing a glass-encapsulated thermistor fabrication process with a wide process window, high yield, effective protection of chip performance, and long-term stability is of great practical significance. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a fabrication process for glass-encapsulated thermistors, solving the problems mentioned in the background section. To achieve the above objectives, this invention employs the following technical solution: A fabrication process for a glass-encapsulated thermistor includes the following steps: S1. Chip and lead preparation: Provide a semiconductor thermistor chip with ohmic contact electrodes formed on its surface, and provide a pair of metal leads with a metal plating layer on their surface; use conductive connecting material to fix the two leads to the two electrodes of the chip respectively to form a chip-lead assembly; S2. Glass encapsulation material preparation: A borosilicate glass powder with a thermal expansion coefficient between that of the thermistor chip material and the metal lead material is provided. The glass powder is mixed with an organic carrier and homogenized to obtain a glass slurry for molding. S3. Coating and Drying: The chip-lead assembly is placed in a molding mold, and the glass paste is used to coat it, so that the paste covers the entire chip and the connection area between the lead and the chip, forming a preform of a predetermined shape; then the preform is dried to remove volatile components in the organic carrier, and a preform with a fixed structure is obtained. S4. Stepped heat treatment packaging: The green body is placed in a programmable temperature control device to execute a heat treatment program containing at least four temperature platforms.

[0007] Preferably, the heat treatment process in S4 includes the following steps: K1, Debinding stage: The green body is heated from room temperature to a first temperature plateau at a first heating rate, and held at the plateau for a first duration to completely decompose and decompose the organic carrier; K2, Pre-sintering stage: The green body is heated from the first temperature platform to the second temperature platform at a second heating rate. The second temperature platform is lower than the softening point of the glass powder, and the temperature is maintained at the platform for a second duration, so that the glass powder particles are initially fused to form a porous skeleton. K3, Sealing stage: The green body is heated from the second temperature platform to the third temperature platform at a third heating rate. The third temperature platform reaches or exceeds the sintering melting temperature of the glass powder, and the temperature is maintained on the platform for a third duration to allow the glass to soften and flow completely, thereby achieving dense encapsulation. K4, Annealing stage: The green body is cooled from the third temperature platform to the fourth temperature platform at a first cooling rate, the fourth temperature platform corresponding to the annealing point temperature range of the glass, and held at the platform for a fourth duration to eliminate internal thermal stress, and then cooled to room temperature to obtain the finished glass-encapsulated thermistor.

[0008] Preferably, the semiconductor thermistor chip in S1 is a negative temperature coefficient (NTC) thermistor chip or a positive temperature coefficient (PTC) thermistor chip; the metal lead wire is made of Dumex wire, Kovar alloy, or iron-nickel-chromium alloy; the metal plating layer is a nickel layer, a gold layer, or a nickel-gold composite layer; the conductive connection material is a conductive adhesive composed of silver paste, copper paste, or gold paste, or a metal welding point formed by spot welding or reflow soldering.

[0009] Preferably, the borosilicate glass powder in S2, by weight percentage, comprises: SiO2: 55% to 70%, B2O3: 15% to 25%, Al2O3: 3% to 8%, Alkali metal oxides (Na₂O + K₂O): 4% to 10%, Alkaline earth metal oxides (selected from one or more of CaO, MgO, and BaO): 1% to 5%, And unavoidable impurities, the total amount of which is less than 0.5%.

[0010] Preferably, the organic binder is at least one of ethyl cellulose, acrylic resin, or polyvinyl butyral; the solvent is at least one of terpineol, butyl carbitol, or terpineol; and the dry weight mixing ratio of the glass powder and the organic carrier is 65:35 to 75:25.

[0011] Preferably, the coating molding method in S3 is injection molding, compression molding, or screen printing layer-by-layer coating molding; the drying temperature is 80°C to 120°C, and the drying time is 1 to 4 hours.

[0012] Preferably, the specific parameters of the stepped heat treatment process in S4 are as follows: K1, Debinding stage: The first heating rate is 1-3℃ / min, the first temperature plateau is 350-450℃, and the first duration is 30-90 minutes; K2, pre-sintering stage: the second heating rate is 2-5℃ / min, the second temperature plateau is 500-600℃, and the second duration is 20-40 minutes; K3, sealing stage: the third heating rate is 3-8℃ / min, the third temperature plateau is 650-750℃, and the third duration is 10-30 minutes; K4, Annealing stage: The first cooling rate is 1-4℃ / min, the fourth temperature plateau is 450-500℃, and the fourth duration is 30-60 minutes; after the heat preservation is completed, it is slowly cooled to below 300℃ at a rate of no more than 2℃ / min, and then naturally cooled to room temperature with the furnace.

[0013] Preferably, during the K4 annealing stage, after the holding time at the fourth temperature platform is completed, the temperature is gradually reduced to 300°C at a rate of 0.5-2°C / min using program control, and then the power is cut off for furnace cooling.

[0014] The advantages of this application are: 1. Excellent stress matching and high reliability: By optimizing the borosilicate glass composition to make its coefficient of thermal expansion between that of chip ceramics and metal leads, and combining it with a precisely controlled annealing process, the residual stress inside the package is greatly reduced, improving the product's crack resistance and long-term reliability under thermal shock.

[0015] 2. Excellent chip performance protection: The stepped heating process of "removal of adhesive - pre-sintering - sealing" avoids the thermal shock and contamination caused by the rapid combustion of organic materials and the rapid melting of glass. The relatively low sealing temperature range (650-750℃) is much lower than the initial sintering temperature of the chip, effectively preventing high-temperature degradation of the chip's semiconductor properties and ensuring the stability of R25 and B values.

[0016] 3. High encapsulation quality: The slow degassing and stepped heating process facilitates gas escape, and combined with sufficient heat preservation time during the sealing stage, the glass body is dense and uniform, with almost no pores, achieving excellent airtightness (up to 10). -8 Pa·m 3 (on the order of / s), thus providing extremely strong moisture-proof and corrosion-proof protection.

[0017] 4. High process controllability and high yield: The entire process parameters are clear and the steps are well-defined. By controlling the slurry viscosity, heating / cooling rate and holding time, the packaging shape and quality can be effectively controlled, making it suitable for large-scale production. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] A fabrication process for a glass-encapsulated thermistor, characterized by comprising the following steps: S1. Chip and lead preparation: Provide a semiconductor thermistor chip with ohmic contact electrodes formed on its surface, and provide a pair of metal leads with a metal plating on their surface; use conductive connecting material to fix the two leads to the two electrodes of the chip respectively to form a chip-lead assembly; The semiconductor thermistor chip in S1 is a negative temperature coefficient (NTC) thermistor chip or a positive temperature coefficient (PTC) thermistor chip; the metal lead wire is made of Dumex wire, Kovar alloy or iron-nickel-chromium alloy; the metal plating layer is a nickel layer, a gold layer or a nickel-gold composite layer; the conductive connection material is a conductive adhesive composed of silver paste, copper paste or gold paste, or a metal solder joint formed by spot welding or reflow soldering.

[0020] S2. Glass encapsulation material preparation: A borosilicate glass powder with a thermal expansion coefficient between that of thermistor chip material and metal lead material is provided. The glass powder is mixed and homogenized with an organic carrier to obtain a glass slurry for molding. The borosilicate glass powder in S2, by weight percentage, comprises: SiO2: 55% to 70%, B2O3: 15% to 25%, Al2O3: 3% to 8%, Alkali metal oxides (Na₂O + K₂O): 4% to 10%, Alkaline earth metal oxides (selected from one or more of CaO, MgO, and BaO): 1% to 5%, And unavoidable impurities, with the total amount of impurities less than 0.5%; The organic binder is at least one of ethyl cellulose, acrylic resin or polyvinyl butyral; the solvent is at least one of terpineol, butyl carbitol or terpineol; the dry weight mixing ratio of glass powder and organic carrier is 65:35 to 75:25.

[0021] S3. Coating and Drying: The chip-lead assembly is placed in a molding mold and coated with glass paste to cover the entire chip and the connection area between the lead and the chip, forming a preform of a predetermined shape; the preform is then dried to remove volatile components from the organic carrier, resulting in a preform with a fixed structure. The overmolding method in S3 is injection molding, compression molding, or screen printing layer-by-layer coating; the drying temperature is 80℃ to 120℃, and the drying time is 1 to 4 hours.

[0022] S4, Stepped heat treatment packaging: The green body is placed in a programmable temperature control device and a heat treatment program containing at least four temperature platforms is executed.

[0023] The heat treatment process in S4 includes the following steps: K1, Debinding stage: The green body is heated from room temperature to a first temperature plateau at a first heating rate, and held at the plateau for a first duration to completely decompose and remove the organic carrier; K2, Pre-sintering stage: The green body is heated from the first temperature platform to the second temperature platform at the second heating rate. The second temperature platform is lower than the softening point of the glass powder, and the temperature is maintained at the platform for a second duration, so that the glass powder particles are initially fused to form a porous skeleton. K3, Sealing stage: The green body is heated from the second temperature platform to the third temperature platform at the third heating rate. The third temperature platform reaches or exceeds the sintering melting temperature of the glass powder, and the temperature is maintained on the platform for a third duration to allow the glass to soften and flow completely, thereby achieving dense encapsulation. K4, Annealing stage: The green body is cooled from the third temperature platform to the fourth temperature platform at the first cooling rate. The fourth temperature platform corresponds to the annealing point temperature range of the glass. The body is held at this platform for a fourth duration to eliminate internal thermal stress. Then it is cooled to room temperature to obtain the finished glass-encapsulated thermistor.

[0024] The specific parameters for the stepped heat treatment process in S4 are as follows: K1, Debinding stage: The first heating rate is 1-3℃ / min, the first temperature plateau is 350-450℃, and the first duration is 30-90 minutes; K2, pre-sintering stage: the second heating rate is 2-5℃ / min, the second temperature plateau is 500-600℃, and the second duration is 20-40 minutes; K3, sealing stage: the third heating rate is 3-8℃ / min, the third temperature plateau is 650-750℃, and the third duration is 10-30 minutes; K4, Annealing stage: The first cooling rate is 1-4℃ / min, the fourth temperature plateau is 450-500℃, and the fourth duration is 30-60 minutes; after the heat holding is completed, it is slowly cooled to below 300℃ at a rate not exceeding 2℃ / min, and then naturally cooled to room temperature with the furnace.

[0025] During the K4 annealing stage, after the holding time at the fourth temperature platform is completed, the temperature is gradually reduced to 300℃ at a rate of 0.5-2℃ / min using program control, or continuously, and then the power is cut off to allow the furnace to cool down.

[0026] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A fabrication process for a glass-encapsulated thermistor, characterized in that, Includes the following steps: S1. Chip and lead preparation: Provide a semiconductor thermistor chip with ohmic contact electrodes formed on its surface, and provide a pair of metal leads with a metal plating layer on their surface; use conductive connecting material to fix the two leads to the two electrodes of the chip respectively to form a chip-lead assembly; S2. Glass encapsulation material preparation: A borosilicate glass powder with a thermal expansion coefficient between that of the thermistor chip material and the metal lead material is provided. The glass powder is mixed with an organic carrier and homogenized to obtain a glass slurry for molding. S3. Coating and Drying: The chip-lead assembly is placed in a molding mold, and the glass paste is used to coat it, so that the paste covers the entire chip and the connection area between the lead and the chip, forming a preform of a predetermined shape; then the preform is dried to remove volatile components in the organic carrier, and a preform with a fixed structure is obtained. S4. Stepped heat treatment packaging: The green body is placed in a programmable temperature control device to execute a heat treatment program containing at least four temperature platforms.

2. The fabrication process of a glass-encapsulated thermistor according to claim 1, characterized in that: The heat treatment process in S4 includes the following steps: K1, Debinding stage: The green body is heated from room temperature to a first temperature plateau at a first heating rate, and held at the plateau for a first duration to completely decompose and decompose the organic carrier; K2, Pre-sintering stage: The green body is heated from the first temperature platform to the second temperature platform at a second heating rate. The second temperature platform is lower than the softening point of the glass powder, and the temperature is maintained at the platform for a second duration, so that the glass powder particles are initially fused to form a porous skeleton. K3, Sealing stage: The green body is heated from the second temperature platform to the third temperature platform at a third heating rate. The third temperature platform reaches or exceeds the sintering melting temperature of the glass powder, and the temperature is maintained on the platform for a third duration to allow the glass to soften and flow completely, thereby achieving dense encapsulation. K4, Annealing stage: The green body is cooled from the third temperature platform to the fourth temperature platform at a first cooling rate, the fourth temperature platform corresponding to the annealing point temperature range of the glass, and held at the platform for a fourth duration to eliminate internal thermal stress, and then cooled to room temperature to obtain the finished glass-encapsulated thermistor.

3. The fabrication process of a glass-encapsulated thermistor according to claim 1, characterized in that: The semiconductor thermistor chip in S1 is a negative temperature coefficient (NTC) thermistor chip or a positive temperature coefficient (PTC) thermistor chip; the metal lead wire is made of Dumex wire, Kovar alloy, or iron-nickel-chromium alloy; the metal plating layer is a nickel layer, a gold layer, or a nickel-gold composite layer; the conductive connection material is a conductive adhesive composed of silver paste, copper paste, or gold paste, or a metal welding point formed by spot welding or reflow soldering.

4. The fabrication process of a glass-encapsulated thermistor according to claim 1, characterized in that: The borosilicate glass powder in S2, by weight percentage, comprises: SiO2: 55% to 70%, B2O3: 15% to 25%, Al2O3: 3% to 8%, Alkali metal oxides (Na₂O + K₂O): 4% to 10%, Alkaline earth metal oxides (selected from one or more of CaO, MgO, and BaO): 1% to 5%, And unavoidable impurities, the total amount of which is less than 0.5%.

5. The fabrication process of a glass-encapsulated thermistor according to claim 1, characterized in that: The organic binder is at least one of ethyl cellulose, acrylic resin, or polyvinyl butyral; the solvent is at least one of terpineol, butyl carbitol, or terpineol; and the dry weight mixing ratio of the glass powder and the organic carrier is 65:35 to 75:

25.

6. The fabrication process of a glass-encapsulated thermistor according to claim 1, characterized in that: The coating molding method in S3 is injection molding, compression molding, or screen printing layer-by-layer coating molding; the drying temperature is 80℃ to 120℃, and the drying time is 1 to 4 hours.

7. The fabrication process of a glass-encapsulated thermistor according to claim 2, characterized in that: The specific parameters for the stepped heat treatment process in S4 are as follows: K1, Debinding stage: The first heating rate is 1-3℃ / min, the first temperature plateau is 350-450℃, and the first duration is 30-90 minutes; K2, pre-sintering stage: the second heating rate is 2-5℃ / min, the second temperature plateau is 500-600℃, and the second duration is 20-40 minutes; K3, sealing stage: the third heating rate is 3-8℃ / min, the third temperature plateau is 650-750℃, and the third duration is 10-30 minutes; K4, Annealing stage: The first cooling rate is 1-4℃ / min, the fourth temperature plateau is 450-500℃, and the fourth duration is 30-60 minutes; After the heat preservation is completed, it is slowly cooled to below 300°C at a rate of no more than 2°C / min, and then naturally cooled to room temperature with the furnace.

8. The fabrication process of a glass-encapsulated thermistor according to claim 7, characterized in that: During the K4 annealing stage, after the holding time at the fourth temperature platform is completed, the temperature is gradually reduced to 300°C at a rate of 0.5-2°C / min using program control, and then the power is cut off to allow the furnace to cool down.